1. Field of the Invention
This invention relates to an air-fuel ratio compensating apparatus for an internal combustion engine which controls the amount of air bleed in a carburetor in relation to the output of an air-fuel ratio sensor.
2. Description of Prior Art
In air-fuel ratio compensating apparatus first and second electromagnetic valves are provided respectively in the air bleed paths of the main and slow fuel supply systems of the carburetor, and the openings of the first and second electromagnetic valves are controlled in relation to the output of the air-fuel ratio sensor. In prior art-fuel ratio compensating apparatus, control current-opening characteristics of the first and second electromagnetic valves are equal to each other and the same control current is sent to the first and second electromagnetic valves from an electronic circuit section. It is preferable that during acceleration of an automobile, fuel is supplied early only from the slow system, and thereafter the fuel supply of the slow system is gradually reduced while fuel supply from the main system is increased, and finally fuel is supplied only from the main system. In such prior air-fuel ratio compensating apparatus, however, the amount of air bleed in the main system is increased during the acceleration period, so the mixture becomes extremely lean and the amount of noxious component in the exhaust is disadvantageously increased. It was previously disclosed that the control current-opening characteristics in the first and second electromagnetic valves could be made different from each other. However in such case, two types of electromagnetic valves are needed which is disadvantageous from a production and assembly standpoint.